1. Field of the Invention
The present invention relates to a captive screw fastener for releasably securing a closure member in the closed position.
2. Description of the Prior Art
Captive screws are used to releasably attach panels over an opening or to secure a door closed. Captive screws have the advantage that once the screw is disengaged from the threaded hole underlying the panel or door to which the captive screw is attached, there are no loose parts that can get lost or fall into crevices in the equipment protected by the door or panel where the impact of the falling screw may even cause damage to sensitive equipment. The captive screw is generally attached to a panel such that the captive screw is in registry with a hole in the panel. The hole in the panel registers with a threaded hole in the structure underlying the panel when the panel is in the closed position. The screw is engaged to the threaded hole to secure the panel in the closed or attached position. The screw is disengaged from the threaded hole to allow the panel to be removed.
The present invention is directed to a captive screw fastener for releasably securing a closure member in the closed position. As an example, the captive screw of the present invention can be used to secure the access panels of electronic equipment over the access openings in such equipment. The captive screw of the present invention includes a screw having a screw head and a shaft having a threaded portion. An annular flange is provided on the shaft intermediate the screw head and the threaded portion of the shaft. The annular flange is spaced apart from the screw head. The captive screw of the present invention also includes a sleeve or ferrule. The ferrule has a hollow bore, a panel engaging end, and a screw retaining end. A portion of the shaft of the screw including the annular flange is housed within the bore of the ferrule with the annular flange being captured between the ends of the ferrule. The screw is movable relative to the ferrule between an extended position and a retracted position. In the extended position the threaded portion of the screw shaft projects from the panel engaging end of the ferrule to its maximum amount. The amount of projection of the threaded portion of the screw shaft from the panel engaging end of the ferrule varies as the screw is moved relative to the ferrule. In the retracted position the amount of projection of the threaded portion of the screw shaft from the panel engaging end of the ferrule is at its minimum. In some embodiments, the threaded portion of the screw shaft may be completely retracted into the bore of the ferrule.
The screw head is located outside the ferrule where it can be accessed by a user""s fingers for tightening or loosening the screw. The screw may be provided with knurling or serration on the peripheral surface of the screw head to give the user""s fingers a better grip. The panel engaging end of the ferrule is designed to engage a hole in the panel that is to be secured by the captive screw in order to attach the ferrule to the panel. The screw retaining end has a hole that allows the shaft of the screw to extend through the hole, however, the diameter of the hole in the screw retaining end of the ferrule is less than the diameter of the annular flange such that the annular flange remains captured within the bore of the ferrule. The screw retaining end of the ferrule may be formed by a second annular flange which projects from the peripheral wall of the ferrule inward toward the central longitudinal axis of the ferrule. The panel engaging end of the ferrule also has a hole that provides clearance for the shaft of the screw but is too small in diameter to allow the annular flange of the screw to clear the opening in the panel engaging end of the ferrule. Peripheral to the hole in the panel engaging end of the ferrule is a shoulder which acts as a seat for one end of an optional spring that may be provided intermediate the annular flange of the screw and the panel engaging end of the ferrule. This optional spring acts to bias the screw toward the retracted position once the screw is disengaged from the threaded hole in the structure underlying the panel. The captive screw of the present invention is attached to a panel such that the screw is in registry with a hole in the panel. The hole in the panel registers with a threaded hole in the structure underlying the panel when the panel is in the closed position. The screw is engaged to the threaded hole to secure the panel in the closed or attached position. The screw is disengaged from the threaded hole to allow the panel to be removed.
In another embodiment, the captive screw of the present invention includes a screw having a screw head and a shaft having screw threads along at least a portion thereof. An annular flange is provided at the base of the screw head. The annular flange has a larger outside diameter than the screw head. The annular flange is contiguous with the screw head and projects radially outward from the base of the screw head. This embodiment of the captive screw of the present invention also includes a sleeve or ferrule. The ferrule has a hollow bore, a panel-engaging end, and a screw-retaining end. A portion of the screw including the annular flange is housed within the bore of the ferrule with the annular flange being captured between the ends of the ferrule. The screw is movable relative to the ferrule between an extended position and a retracted position, and the range of motion of the screw relative to the ferrule is limited by the range of motion of the annular flange within the ferrule. In the extended position at least some of the threaded portion of the screw shaft projects from the panel-engaging end of the ferrule. The amount of projection of the threaded portion of the screw shaft from the panel-engaging end of the ferrule varies as the screw is moved relative to the ferrule. In the retracted position the amount of projection, if any, of the threaded portion of the screw shaft from the panel-engaging end of the ferrule is at its minimum. This means that in some embodiments the threaded portion of the screw shaft may be completely retracted into the bore of the ferrule.
The screw head is accessible from outside the ferrule, thus allowing a user to turn the screw using any suitable tool. The panel-engaging end of the ferrule is designed to engage a hole in a panel in order to attach the ferrule to the panel. The screw-retaining end has a hole that allows the top portion of the head of the screw to extend through the hole. However, the diameter of the hole in the screw-retaining end of the ferrule is less than the diameter of the annular flange such that the annular flange remains captured within the bore of the ferrule. The panel-engaging end of the ferrule also has a hole that provides clearance for the shaft of the screw but is too small in diameter to allow the annular flange of the screw to clear the opening in the panel-engaging end of the ferrule. Peripheral to the hole in the panel-engaging end of the ferrule is a shoulder that acts as a seat for one end of a spring that may be provided intermediate the annular flange of the screw and the panel-engaging end of the ferrule. This optional spring acts to bias the screw toward the retracted position once the screw is disengaged from the threaded hole in the structure underlying the panel. As with the previous embodiment, this embodiment of the captive screw of the present invention is attached to a panel such that the screw is in registry with a hole in the panel. The hole in the panel is positioned in registry with a threaded hole in the structure underlying the panel when the panel is in the closed position. The screw is engaged to the threaded hole to secure the panel in the closed or attached position. The screw is disengaged from the threaded hole to allow the panel to be removed.